The province is expanding eligibility for booster shots of the COVID-19 vaccine to around 2.75 million high-risk Ontarians, but the general population won't be able to get boosters before the new year.
The updated list of eligible Ontarians includes adults 70 and over, health-care workers, Indigenous adults and their non-Indigenous household members, essential caregivers in congregate settings and individuals who received two doses of the AstraZeneca vaccine or one dose of the Janssen vaccine.
Ontario said it included the first three groups due to an "increased risk of gradual waning immunity," with older adults facing a higher risk of severe disease, health workers having a higher risk of exposure and a shorter interval between their first and second doses, and Indigenous communities being disproportionately affected by COVID-19. Those who received a viral vector vaccine were included because they "started with a lower vaccine efficacy" and could see decreasing immunity sooner than those who received an mRNA dose, the government stated.
Chief Medical Officer of Health Dr. Kieran Moore said studies show that a booster dose of an mRNA vaccine produce "a very good immune response that is generally higher than the immune response after the primary series."
A booster dose has "a favourable safety profile" and offers "good short-term protection against infection," he added. 
Eligible individuals will be able to start booking their booster dose on Nov. 6 at 8 a.m. through the province's online vaccine portal and call centre, through local public health units and select pharmacies. While some primary care providers will be able to deliver booster shots, they will be contacting patients directly. Either mRNA vaccine — Pfizer or Moderna — can be used for the booster shot, the government said.
The province plans to gradually expand eligibility to all Ontarians over time and expects to start this in the new year, but is waiting for clinical recommendations from NACI and Ontario's immunization advisory committee, government officials said during a media briefing. The government anticipates booster doses for the general population will be offered six to eight months after second doses.
"At a population level we still, five to seven months out after our second doses, have very good, prolonged protection for all Ontarians, the data is showing very good protection against severe outcomes or hospitalization," said Moore. 
The province said its plan of offering booster shots to additional groups aligns with recommendations from the National Advisory Committee on Immunization (NACI). The committee recommended on Sept. 28 that a booster shot of the COVID-19 vaccine be offered to seniors in long-term care and other congregate settings at least months after their second dose. In updated guidance on Oct. 29, NACI said boosters should also be offered to adults 80 and older and may be offered to other groups including adults 70–79, those who got two doses of the AstraZeneca vaccine or one dose of Janssen, adults in or from Indigenous communities and front-line health-care workers who have direct contact with patients.
Ontario started rolling out third doses to some Ontarians in August including long-term care residents,  seniors in higher-risk retirement homes and immunocompromised individuals like transplant recipients or those with hematological cancers.
On Sept. 14 that list was expanded to include other groups facing the "highest risk of serious illness" from COVID-19 including people undergoing treatment for solid tumors or those being treated with immunosuppressive therapies like high-dose systemic corticosteroids. Seniors in all retirement homes and congregate care settings were added in October.
So far more than 250,000 Ontarians have been eligible to receive a booster shot or a third dose, with more than 161,000 doses being administered so far.
Moore said the government is not mandating any change to the vaccine passport system, so two doses will still be accepted to get into venues that have vaccine restrictions.
Doris Grinspun, CEO of the Registered Nurses' Association of Ontario, welcomed the government's announcement, noting that nurses and other health workers continue to be on the front lines, working with COVID-19 patients and individuals who are immunocompromised.
"They're welcoming this because it protects them, it protects their families and communities and also what we wanted all along, which is to protect patients," said Grinspun, adding that offering a booster to more seniors, including those in the community, is "extremely important."
Grinspun said now she looks forward to the vaccination of children, adding that she hopes the province can roll them as soon as possible if they're approved.
The province said it expects a decision regarding vaccines for five to 11-year-olds this month and that all public health units will offer select school-based vaccination sites. Other possible sites include mass immunization clinics, pharmacies, primary care providers, children's hospitals and mobile teams.

Ontario expanding booster shots to adults 70 and older, health-care workers

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